1. Field of the Invention
This invention relates generally to non-propulsive fin control in an air or sea vehicle and, more particularly, to such a method and apparatus using planar actuation.
2. Description of the Related Art
An air or sea vehicle's control system provides a mechanism to control the vehicle's direction of travel. The directional control may be accomplished by directing the vehicle to travel with a particular vehicle attitude with respect to the relative movement through a fluid in which the vehicle is traveling. Typically the control system, whereby the non-propulsive fins are independently commanded, provides the attitude control required to traverse a given path.
A vehicle's attitude can be divided into roll, pitch, and yaw attitudes. The control of the vehicle's attitude can be theoretically realized through the use of three fins to control the vehicle's roll, pitch, and yaw attitudes. Typically, however, four fins are implemented, and occasionally five or more are used.
The number of fins implemented depends on the vehicle's application. Increasing the number of fins will in turn increase the amount of control force the fins will provide. However, increasing the fin control force does not necessarily increase the maneuverability of the vehicle. Increasing the number of fins in a traditional manner will also increase the weight and complexity of the vehicle, which may offset the increased control force produced.
The vehicle's roll, pitch, and yaw attitudes can be controlled by rotating the fins in a predetermined fashion to obtain a desired vehicle attitude, regardless of the number of fins. Typical implementations use a separate actuator for each fin so that each fin may be commanded independently. The use of separate actuators for each fin has some undesirable effects. For instance, separate actuators increase vehicle weight, complexity and the possibility of relative fin rotation error. Minimizing vehicle weight is a high priority in vehicle design because vehicle mass directly contributes to maneuverability potential. Slight increases in mass can make significant changes in vehicle agility and/or range performance. Decreasing vehicle complexity is important from a standpoint of vehicle reliability and cost. Reduced complexity designs are in general less costly to produce and operate more reliably than higher complexity designs. Control system relative rotation error is induced when individual actuators per fin are employed because of positional errors associated with each actuator. The positional errors can corrupt the desired relative rotation angles between fins and induce error into the commanded roll, pitch, and yaw attitudes.
The present invention is directed to overcoming one, or more, of the problems set forth above.